g1smd - 5:59 pm on May 13, 2012 (gmt 0)

They'll eventually be flagged as having low technical quality.

some show a 404 then redirect

What do you mean by that?
- Return a 404 status code in the HTTP header then perform a meta refresh to some other URL?
- Show the words "404 Not Found" on the page while returning a different status code in the HTTP header?

After returning a HTTP 404 status code, that's the end result. It's not possible to perform a HTTP redirect after that.

The only way to see multiple status codes is if the first one is a 30x redirect. There may be multiple redirects in a chain, and that's bad too. The final code will be a 2xx or 4xx code.